Conventionally, it has been proposed to use silicon carbide (SiC) as a material for a semiconductor device. For example, it has been proposed to form a trench gate-type MOSFET using silicon carbide (see Japanese Patent Laying-Open No. 2008-235546 (Patent Literature 1)).
Japanese Patent Laying-Open No. 2008-235546 proposes forming a trench having a gate electrode and a gate insulating film arranged therein to have a tapered side wall in order to improve breakdown voltage of the gate insulating film in a trench gate-type MOSFET. Specifically, by removing a portion of a semiconductor layer made of silicon carbide by anisotropic etching using an etching mask having an opening pattern, and thereafter performing isotropic etching, a trench is formed in the semiconductor layer to have a tapered side wall.